There are four different types of content on Tableau Server: 

• Projects: The highest level; it is like a folder. You can only create new projects from the web. A project can contain other Sub-Projects, Workbooks, and Data Sources.
• Workbooks: Either created on Tableau Desktop and published here, or directly created in Tableau Server. Each Workbook is composed of one or multiple Views.
• Views: All the different Worksheets, Dashboards, and Stories in the Workbooks.
• Data Sources: Created on Tableau Desktop and published here. You can use them to build new analyses directly on the web.

Tableau Server has two ways of displaying Content. Since the 2018.3 version, the default way is called Mixed Content and shows different types of Content in the same place.

As you can see in the following screenshot, in the Sales project, there is one other Sub-Project, one Workbook, and one Data Source, all displayed in the same place:

Before Tableau Server 2018.3, the different types of Content were separated into different tabs, and you needed to select a specific tab to see its Content. You can see, in the following screenshot, the same Sales project, traditionally displayed:

Let's look at how to publish Data Sources and Workbooks from Tableau Desktop.